1. Field of Invention
This invention relates to improvements in the sweetening of sour, gaseous hydrocarbons, liquid hydrocarbon condensates, or crude petroleum products in a treating tower, or in a pipeline, or at the well-head or collection point in an oil or gas field, and more particularly to an improved method for sweetening by oxidation.
2. Brief Description of Prior Art
The production of gaseous or liquid hydrocarbons often requires the separation or removal of various contaminants from these streams before they can be transported for further use. These petroleum components usually contain substantial quantities of entrained water and other gaseous and liquid hydrocarbon condensates containing toxic constituents, which subsequently must be removed.
Gaseous hydrocarbons contain other gaseous impurities, which are acids in aqueous solutions, and are thus corrosive in nature. Hydrogen sulfide and other organic sulfides, which are very toxic and malodorous are otherwise termed as toxic, sour systems. Hydrogen sulfide (H.sub.2 S) is more toxic than hydrogen cyanide (HCN) and presents a further problem that it is highly malodorous in very low concentrations and tends to anesthetize the olfactory nerves with the result that a toxic exposure may not be recognized until it is too late. The removal or neutralization of H.sub.2 S is therefore a matter of necessity!
One process for removal of H.sub.2 S and other organic sulfides entails a solid/gas chemical reaction. An iron-sponge, consisting of a hydrated iron oxide on an inert support, is treated with the sour gaseous system converting the iron oxide to the sulfide, i.e., iron pyrites. Exposure of wet iron sulfide to air, as it is removed from the bubble-tower, may cause a pyrophoric condition to exist resulting in a fire.
Some physical processes for removal of H.sub.2 S and organic sulfides require solid clays such as molecular sieves, i.e., zeolites and other materials having pore sizes in molecular dimensions which are specific for removal of H.sub.2 S and CO.sub.2. These types are used in the form of a bed through which the sour gaseous or liquid mixture is passed. The bed is periodically regenerated by stripping with an inert gas. This process has the disadvantage present in most desulfurization processes in that the separated H.sub.2 S or organic sulfides must be disposed of in the field by flaring or other mechanical means.
Other processes for removal of H.sub.2 S and organic sulfides involves the use of strong oxidizers at high concentrations. These processes have been expensive in using large amounts of expensive oxidizers.
Systems have been developed wherein chemical scavengers are injected by in-line techniques without the obvious disadvantages described above. A brief history of these types of scavenging agents will be presented below.
Materials used with such in-line injection techniques include various aldehydes. H.sub.2 S reacts rapidly and completely with aidehydes to form a variety of addition compounds, such as polyethylene sulfide, polymethylene disulfide and trithiane. Such a process was disclosed in the following publication: Walker, J. F., "FORMALDEHYDE", Rheinhold Publishing Co., New York, page 66,(1953).
Alkanolamines are widely used in systems that adsorb H.sub.2 S as disclosed above. These in-line injection systems are in use throughout the oil and gas industry. U.S. Pat. No. 2,776,870 discloses a process for separating acidic components from a hydro-carbon mixture comprising adding to the mixture of hydrocarbons an absorbent containing water-soluble aliphatic amines and Alkanolamines, preferably monoethanolamine. However, Alkanol-amines are not selective in their reaction with H.sub.2 S and CO.sub.2 in that, they react with all acidic components present in these hydrocarbon mixtures removing both H.sub.2 S as well as CO.sub.2. Such non-selectivity is not desirable in many applications and therefore the usage of alkanolamines has come under disfavor for this reason.
Baize U.S. Pat. No. 4,748,011, Dillon U.S. Pat. No. 4,978,512, Vasil U.S. 5,314,672 and Weers European patent 411,745 are representative of processes using amine-formaldehyde reaction products for sweetening sour natural gas by in-line or well-head injection.
Lonnes U.S. Pat. No. 3,969,479 discloses a method for oxidizing odorous constituents of contaminated gas in rendering plants, fish processing plants, asphalt plants, and other plants in which aldehydes, fatty acids, ketones, mercaptans, amines, hydrogen sulfide, sulphur dioxide, nitric oxide, phenols or other pollutants are emitted. Chlorine in the form of sodium hypochlorite in a concentration of 5-50 ppm is the preferred oxidizing agent. Consumption of the oxidizing agent is minimized by continuously purging 1-5% of the scrubbing liquid to thereby promptly remove precipitates and other solids.
Banasiak U.S. Pat. No. 4,049,775 discloses a method for purifying waste air from sulfuric gases, in particular from hydrogen sulfide, carbon disulfide and sulfur dioxide by adsorption and oxidation in a bath containing inorganic oxidizing compounds soluble in water, e.g. hypochlorites of alkali metals, preferably sodium hypochlorite and a catalyst at pH of 9-12 in a dosed cycle of bath.
Brown U.S. Pat. No. 4,361,487 discloses removing hydrogen sulfide from geothermal steam condensate by oxidizing with a peroxygen compound such as hydrogen peroxide in the presence of catalytic quantities of sodium vanadate under neutral to alkaline conditions.
Oakes U.S. Pat. No. 4,473,115 discloses a method for reducing concentrations of hydrogen sulfide present in subterranean well fluids by injection of a stabilized solution of chlorine dioxide.
Meisel U.S. Pat. No. 4,548,708 discloses a process for substantially complete elimination of hydrogen sulfide from the organic phase of natural gas, crude oil or mixtures thereof, by reaction with aqueous hydrogen peroxide in the absence of any catalyst.
Chelu U.S. Pat. No. 4,550,010 discloses a process for deodorizing polluted air, wherein the air to be deodorized is washed in a washing apparatus with an aqueous solution of hydrogen peroxide.
Brunasso U.S. Pat. No. 5,047,218 gas containing sulfur compounds being admixed with an ozone-containing gas, then contacted with a scrubbing composition to obtain a gas and a product solution. The gas exhibits a significant reduction in sulfur compounds as compared to the feed gas.
These oxidative processes are all objectionable is using excessive amounts of expensive oxidants.